If peak inspiratory pressure rises while the plateau pressure remains the same during ventilation with a constant tidal volume, which parameter is most likely increasing?

• A. Increased lung compliance
• B. Increased airway resistance
• C. Decreased airway resistance
• D. Increased tidal volume

Answer: (B)

Peak inspiratory pressure reflects both the force needed to expand the lungs (lung compliance) and the force required to push gas through the airways (airway resistance). Plateau pressure, measured with an inspiratory hold, represents the elastic load of the lung/chest wall (compliance) and is not affected by airway resistance. When tidal volume is held constant and peak inspiratory pressure rises but plateau pressure stays the same, the extra pressure must be overcoming greater airway resistance rather than expanding the lungs. In other words, airway resistance has increased (for example, bronchospasm, secretions, or a kinked endotracheal tube), while lung mechanics are unchanged. Changes in compliance would alter plateau pressure, and changing tidal volume would alter pressures as well, so those scenarios don’t fit this pattern.